When an electromagnetic wave is propagated in high dielectric constant substances, a wavelength of the electromagnetic wave will be shortened, by using this characteristic, the traditional metal materials can be replaced with dielectric materials (such as ceramics), under the same index, a volume of the filter can be lessened. The research on the dielectric filter is always a hotspot in the communications industry. Since the filter serves as a major component of wireless communication products, the dielectric filter plays a particularly important role in the miniaturization of the communication products.
Generally, the dielectric filter is mainly composed of dielectric resonant cylinders 103, a sealing cover plate 102, a tuning screw 101 and a metal cavity 104, with reference to FIG. 1.
According to a working principle of a TM mode dielectric resonant cavity, when a dielectric resonator normally operates, high electric-field distribution exists in a binding site between lower end faces of the cylindrical dielectric resonant cylinders 103 and the metal cavity 104. If the contact between the lower end faces of the dielectric resonant cylinders and the metal cavity 104 is insufficient, discontinuous impedance will be caused, field energy cannot be transmitted out, a high dielectric constant and high quality factor of the medium cannot be brought into play, and even the medium will be burn up. Therefore, whether the contact between the lower surfaces of the dielectric resonant cylinders and the surface of the metal cavity is good in a TM mode dielectric filter is especially crucial. How to solve the fixation and contact of the TM mode dielectric resonant cylinders becomes a key research direction of the dielectric filter application.
With reference to FIG. 1, lower end faces of two nonmetal dielectric resonant cylinders whose lower ends are coated with a metal layer (such as ceramics) or lower end faces of metal resonant cylinders 103 are directly welded on the metal cavity 104, which is used for close contact with the undersurface of the metal cavity. The sealing cover plate 102 seals the metal cavity 104 through the screw, to form a hermetic cavity. Since directly welding the dielectric resonant cylinders on the undersurface of the metal cavity has extremely high requirements for welding technology, there is a shedding phenomenon in the entire dielectric resonant cylinder welding process, which severely affects the performance and service life of the dielectric filter.
A TM mode dielectric filter in the related art includes a metal resonant cavity, a cover plate, a tuning screw and a TM mode dielectric resonator, the TM mode dielectric resonator is fixed within the metal resonant cavity through the screw, it is characterized in that, a screw rod part of the screw passes through a location hole of the TM mode dielectric resonator to be screwed down on the bottom or side wall of the metal resonant cavity, the screw rod part of the screw is not in contact with a hole wall of the above location hole, and a transition gasket is set between the head of the screw and the end face of the location hole of the TM mode dielectric resonator to separate them. The assembly technology is complicated in the specific implementation process of the patent, which has higher requirements on structure design, exerts greater impact on the performance, goes against volume production, and has high costs.